The present invention relates to an improvement in the flexpins used for securing large earth excavation teeth to the nosepiece of the adaptor attached to the shovel or excavating bucket of the excavation equipment. The securement pins commonly used for such applications are ellipsoidal in cross section and comprise two elongate steel alloy members secured by a hard resilient rubber or silicone center. U.S. Pat. No. 4,516,340 describes such a pin and its use in detail. Briefly, each elongate member defines a beveled forward nose portion to facilitate insertion of the pin through the aligned orifices in the excavation tooth and the slightly offset channel in the adaptor and a flat heel portion to present a blunt surface to the hammer or other implement used to drive the pin into place. The central portions of the two elongate members are offset relative to the nose and heel portions to provide annular abutment shoulders for engaging portions of the excavation tooth and adaptor about the orifices and channel through which the pin extends to hold the pin in place during use and thereby secure the tooth to the adaptor. The generally elliptical or round opening through the tooth and adaptor which receives the pin defines a major axis somewhat less than the major axis of the securement pin so that the pin must be compressed about its resilient center as it is driven into place. Once in place the compressed center urges the two steel elongate member on either side thereof against the side walls of the tooth orifices and adaptor channel with sufficient strength to rigidly affix the tooth to the adaptor. The strength required of such pins to achieve this result, however, does create certain problems, particularly with respect to pin insertion and removal.
Because of the tremendous forces exerted on these pins during use, they must be extremely strong and durable. They must also provide a very tight securement between the tooth and adaptor as relative movement therebetween will tend to move the pin which fatigues the rubber center and causes premature product failure. While these securement pins vary in size depending on the size of the bucket and digging teeth with which they are used, they must often be quite large to have the necessary strength and provide the tight securement required for large excavation teeth. For example, a mounting adaptor can often weigh about 700 lbs. and carries excavation tooth weighing about 185 lbs. A typical securement pin for such an assembly is about 2.25.times.1.5 inches in cross section, 9.5 inches in length and weighs about 6 lbs. To install such pins in these assemblies under normal conditions requires two men and the use of a 16 lb. sledge hammer due to the necessary size of the pin, the compression required to effect insertion and the large surface areas thereon which bear tightly against the tooth and adaptor and collectively provide the strength and securement forces necessary to retain the tooth firmly in place during use. When these excavation teeth become worn and require replacement, the pin must be removed which again requires two men and is typically even a more difficult task as the pin also has become worn, deformed and has dirt and rock fines lodged between the pin and adjacent surfaces. Failure to meet tight tolerances in the manufacture of the tooth, adaptor or pin can make installation and removal even more difficult or result in inadequate tooth securement and product failure. In addition, the forces exerted on the pin during installation and removal by such a large hammer can fracture the heel of the pin, causing steel chips to fly therefrom and create a significant safety hazard for a nearby personnel.
Despite the size of these flexpins, the forces exerted thereon during use can be so large that they can bend the backside of the pin which is defined by the rearwardly disposed steel elongate member. When this occurs, the pin can be driven or "jacked" upwardly or downwardly from its securement position causing product failure. This typically occurs in difficult excavation applications employing hydraulic, backhoes and shovel designs wherein the forces are exerted on both the upper and lower surfaces of the excavation tooth. Because of the configurations of the mating component parts, such forces are relatively isolated and are transmitted directly to the backside of the upper and lower regions of the rear portion of the flex pin against which the tooth bears and, despite the solid steel construction of the rearwardly disposed elongate member, causes a bending thereof. As the upper and lower end portions of the rear elongate member on the flex pin are pushed forwardly, the pin looses it locking engagement on its backside with the excavation tooth, allowing the pin to be jacked upwardly or downwardly relative to the tooth and adaptor depending on the movement of the tooth through the earth, ultimately resulting in tooth loss or failure. Even when tooth loss does not occur, such bending of the pin during use, like the sheer forces exerted on the rubber center portion thereof during installation and removal, tends to deteriorate the rubber center of the pin. Deterioration of the rubber also results in a loss of locking power and can accelerate the tendency of the pin to jack out also during use.
The pin assembly of the present invention provides an economical solution to each of the aforesaid problems inherent in the securement flexpins employed in the attachment assemblies for large earth excavation teeth without sacrificing any of the benefits of such pins or requiring modification of either the teeth or mounting adaptors currently in use.